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b=RQrmE5/7IQ9bHGm6Pg5nzKRS/MrnD7O62plkaE4ISC71znarStIv1c+rqH2eD21Ay BoSVycIDYj6++q91gMxaMW8tzGjKmn+SvAyr1OTzL/FcJ36O6uFSlSjO6ZPcwy46CK V9IseUAeKcQzyanwocprzA2s51mzkrUD5ABcIT8OciKKvQNnsEU880OUUzVK34Htru u6aYBYybBkBP3b7teFgYlIwGLVHKsTDk0UBcHC5zheI0DFrGgbp8BVZ6lqSWQUnKpR MaQvJ7GxK0lGxJqjJszIHK7PI7DUNxOXr5WfircZfyz086GeBt2U1zKAGDhFX3U5YY JKj3OO3SKnwhA== From: Michael Ellerman To: Andrew Morton , David Laight Cc: "glider@google.com" , "elver@google.com" , "zhangpeng.00@bytedance.com" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linuxppc-dev@lists.ozlabs.org" Subject: Re: [PATCH] mm: kfence: Fix false positives on big endian In-Reply-To: <20230517152028.86b6d2d5afa4541b4269131b@linux-foundation.org> References: <20230505035127.195387-1-mpe@ellerman.id.au> <826f836f41db41eeb0fc32061994ac39@AcuMS.aculab.com> <20230517152028.86b6d2d5afa4541b4269131b@linux-foundation.org> Date: Fri, 19 May 2023 15:14:06 +1000 Message-ID: <87o7mgzyw1.fsf@mail.lhotse> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 6ECF340012 X-Stat-Signature: r16r787ewf8ys3mrmpza8aaztjsh6pty X-Rspam-User: X-HE-Tag: 1684473254-791248 X-HE-Meta: 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 DBIPlYcG 1UK0vd0vw+SEIsjR5hS5dyFOugG3g9bpfPQyx1nAYXeM1wpIS8MYDrresViNj/taSbOcl58U0+wYGYwaN223K/9dd+PaELai4FNYmYAS+hNHtWwuyJeYjegLY8AztfKblVxzQz2ZuHSW1wQrNS2jMyaoP8rDxkfVQ1m3yhxxNPqswsCfVOB0sVefVe4Dce4T1lqCAfmVigsAL7aMFw+rMm4Ds/y3yg2rku7DzsSvTvrLTjCdlovtuGNWGmOipfMzu93L57rkCikCis55YE2C0TMXVxlsPjnoACqnISaL5wadezsIDkgX1ZgpoZJGiPppU1D4HDaM5l1wYWTs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Andrew Morton writes: > On Fri, 5 May 2023 16:02:17 +0000 David Laight wrote: > >> From: Michael Ellerman >> > Sent: 05 May 2023 04:51 >> > >> > Since commit 1ba3cbf3ec3b ("mm: kfence: improve the performance of >> > __kfence_alloc() and __kfence_free()"), kfence reports failures in >> > random places at boot on big endian machines. >> > >> > The problem is that the new KFENCE_CANARY_PATTERN_U64 encodes the >> > address of each byte in its value, so it needs to be byte swapped on big >> > endian machines. >> > >> > The compiler is smart enough to do the le64_to_cpu() at compile time, so >> > there is no runtime overhead. >> > >> > Fixes: 1ba3cbf3ec3b ("mm: kfence: improve the performance of __kfence_alloc() and __kfence_free()") >> > Signed-off-by: Michael Ellerman >> > --- >> > mm/kfence/kfence.h | 2 +- >> > 1 file changed, 1 insertion(+), 1 deletion(-) >> > >> > diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h >> > index 2aafc46a4aaf..392fb273e7bd 100644 >> > --- a/mm/kfence/kfence.h >> > +++ b/mm/kfence/kfence.h >> > @@ -29,7 +29,7 @@ >> > * canary of every 8 bytes is the same. 64-bit memory can be filled and checked >> > * at a time instead of byte by byte to improve performance. >> > */ >> > -#define KFENCE_CANARY_PATTERN_U64 ((u64)0xaaaaaaaaaaaaaaaa ^ (u64)(0x0706050403020100)) >> > +#define KFENCE_CANARY_PATTERN_U64 ((u64)0xaaaaaaaaaaaaaaaa ^ (u64)(le64_to_cpu(0x0706050403020100))) >> >> What at the (u64) casts for? >> The constants should probably have a ul (or ull) suffix. >> > > I tried that, didn't fix the sparse warnings described at > https://lkml.kernel.org/r/202305132244.DwzBUcUd-lkp@intel.com. > > Michael, have you looked into this? I haven't sorry, been chasing other bugs. > I'll merge it upstream - I guess we can live with the warnings for a while. Thanks, yeah spurious WARNs are more of a pain than some sparse warnings. Maybe using le64_to_cpu() is too fancy, could just do it with an ifdef? eg. diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h index 392fb273e7bd..510355a5382b 100644 --- a/mm/kfence/kfence.h +++ b/mm/kfence/kfence.h @@ -29,7 +29,11 @@ * canary of every 8 bytes is the same. 64-bit memory can be filled and checked * at a time instead of byte by byte to improve performance. */ -#define KFENCE_CANARY_PATTERN_U64 ((u64)0xaaaaaaaaaaaaaaaa ^ (u64)(le64_to_cpu(0x0706050403020100))) +#ifdef __LITTLE_ENDIAN__ +#define KFENCE_CANARY_PATTERN_U64 (0xaaaaaaaaaaaaaaaaULL ^ 0x0706050403020100ULL) +#else +#define KFENCE_CANARY_PATTERN_U64 (0xaaaaaaaaaaaaaaaaULL ^ 0x0001020304050607ULL) +#endif /* Maximum stack depth for reports. */ #define KFENCE_STACK_DEPTH 64 cheers